DNS Resolving large number of reverse entries all the time

Hello,
I just setup a DNS server , and it is resolving fine.
I have also applied all sort of relevant ACL in order to block all other traffic only port 53 is open.
Wat i am experiencing is, My DNS is resolving large number of reverse entries all the time ranging in 10K.
ALl the Source IPs are of different region ..
kindly expalin me why other international ISPs/Web server using my dns server to resolve secondly why my reverse entries are so high.

I would recommend that you disable recursion on your external DNS server(s), unless you are acting in the capacity of an ISP and are trying to provide a service to your customers. Otherwise, you really dont want anyone to be successfully querying your box for records other than those you are authoritative for.